Rotate an Array using Reverses

Computer Science Level 3

Given an array A A and a number k k

We can rotate A A by k k spots.

For example

Given: 

1
2
 
A = [1, 2, 3, 4, 5]
k = 3

We would get: 

1
 
[4, 5, 1, 2, 3]

This can be done using a series of reverses.

How many calls to reverse() would you need?


The answer is 3.

フランスワ 砂取 by フランスワ 砂取 , 31, Canada

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1 solution

Henry U
Nov 10, 2018

Let the lenght of A A be l l .

  1. Reverse the whole array
  2. Reverse the first l − k l-k elements, with indices { 0 , … , l − k − 1 } \{0, \ldots, l-k-1 \}
  3. Reverse the last l − k l-k elements, with indices { l − k , … , l − 1 } \{l-k, \ldots, l-1\}
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